My sister keeps on teasing me about me being Anorexic........?

Aww that's sad that your sister says that stuff to you. I recommend that you tell your sister how your feeling or she'll never stop. To her, she probably thinks its just a joke. And don't feel too down, I can really relate to you. Im 12, 5"2, I weigh 80 pounds though. My family always makes fun of me...but I really don't care because its better to be skinny than fat. Think of it that way. I bet a lot of fat girls are really wishing they were you right now. And girl, wear your tankini like you own it! Don't worry about what anyone thinks or says about you!